Secondary Dominants and Applied Chords

Harmonic progression is more than just moving from one chord to the next within a key; it’s about creating direction, tension, and color. Secondary dominants are one of the most powerful tools composers use to temporarily heighten the importance of a chord that is not the tonic, injecting chromaticism and driving momentum. Mastering how to identify, analyze, and hear these chords is a cornerstone of intermediate and advanced harmonic analysis, directly tested on the AP Music Theory exam.

The Core Concept: Tonicizing a New Chord

In any major or minor key, the most powerful harmonic motion is the dominant chord (V) resolving to the tonic (I). A secondary dominant applies this same powerful V-to-I relationship to a chord other than the true tonic. This process is called tonicization—momentarily making another chord sound like a temporary tonic. For example, in the key of C major, the V chord is G major. The V of the V chord (written V/V) would be the dominant chord that leads to G major. The dominant of G major is D major. Therefore, in the key of C, a D major chord functioning as V/V creates a strong pull toward the G major chord, temporarily treating G as if it were "home."

Any diatonic chord (a chord built from notes within the key) can be preceded by its own secondary dominant. The most common secondary dominants are those that tonicize chords that are already major or minor in the key, such as V, ii, iii, IV, v, and vi. You cannot tonicize a diminished chord (like vii° in major) with a standard dominant seventh chord, as a proper dominant-tonic resolution requires a major triad or a minor triad as the temporary tonic.

Notation and Identification

Accurate identification in Roman numeral analysis is crucial. The standard notation is "V/x" or "V7/x," where the chord after the slash is the chord being tonicized. This chord is called the secondary tonic or temporary tonic.

• V/V (Five of Five): In C major, this is a D major chord (D-F#-A) leading to G major.
• V7/vi (Dominant Seven of Six): In C major, this is an E7 chord (E-G#-B-D) leading to A minor.
• V/IV (Five of Four): In C major, this is a C7 chord (C-E-G-B♭) leading to F major. Note how this secondary dominant (C7) differs from the actual tonic chord (C major).

The key signature does not change. Instead, you use accidentals to create the necessary leading tone for the temporary tonic. The most important note in any secondary dominant is the chromatic leading tone it introduces. For V/V in C major, the F# is the chromatic leading tone that strongly pulls up to the root (G) of the temporary tonic.

Resolution and Voice Leading

Secondary dominants resolve with the same strong, conventional voice-leading as primary dominants. The leading tone (the third of the secondary dominant) should resolve upward by half step to the root of the temporary tonic. The seventh of a secondary dominant seventh chord (if present) should resolve downward by step.

Let's examine V7/vi to vi in C major (E7 to Am).

• The chord tones of E7 are E (root), G# (third), B (fifth), D (seventh).
• The chord tones of A minor are A (root), C (third), E (fifth).
• G# (the chromatic leading tone for A) resolves up to A.
• D (the seventh) resolves down to C.
• B can resolve to either A or C.
• E can be held as a common tone or move to E.

This smooth, predictable resolution is what makes the progression sound logical and satisfying, even with the introduced chromaticism.

Extended Applications: Chains and Deceptive Resolutions

The concept can be extended to create longer tonicizing sequences. A chain of secondary dominants occurs when one secondary dominant resolves to another chord, which is itself immediately treated as a new temporary tonic by another secondary dominant (e.g., V/V/V). While less common, it demonstrates the flexibility of the principle.

Furthermore, secondary dominants can also take deceptive resolutions. Just as V7 can deceptively resolve to vi instead of I, a V7/vi could deceptively resolve to IV instead of vi. This provides composers with a way to introduce the color and tension of a secondary dominant without fulfilling the expected harmonic motion, creating surprise.

Common Pitfalls

Misidentifying Non-Functional Chromatic Chords: Not every chromatic chord is a secondary dominant. A chord like D major in the key of C could be a secondary dominant (V/V), but it could also be part of a modal mixture (borrowed from C minor) or a non-functional chromatic passing chord. The definitive test is function: Does it resolve directly and convincingly down a perfect fifth (or up a perfect fourth) to a diatonic chord, using proper voice leading? If it doesn't resolve as a dominant, it isn't functioning as one.

Incorrect Roman Numeral Analysis: A common error is to simply write the chord's root in Roman numerals based on the home key. In C major, a D major chord is not "II." The uppercase "II" implies a diatonic chord, which in C major would be D minor. You must use the secondary dominant notation (V/V) to accurately convey its harmonic function. On the AP exam, failing to use the slash notation will cost you points.

Overlooking the Temporary Tonic: When you see a secondary dominant, always ask, "Where is it going?" The secondary tonic chord is an integral part of the analysis. Isolate the two-chord progression (e.g., V7/vi - vi) to ensure the resolution is sound. If the expected temporary tonic chord is altered or absent, you may need to re-evaluate your analysis.

Summary

• Secondary dominants are chromatic chords that function as the dominant (V or V7) of a scale degree other than the original tonic, creating a momentary tonicization.
• They are identified in analysis with slash notation (e.g., V/V, V7/vi), where the chord after the slash is the temporary tonic being targeted.
• Their analysis depends on function and resolution: they must resolve with strong voice-leading (especially the chromatic leading tone) down a fifth to a diatonic chord.
• They introduce compelling chromatic color and directional tension into a progression without permanently leaving the original key.
• For the AP Music Theory exam, practice both identifying them in written scores and hearing their distinctive sound—a chromatic "lift" followed by a strong, satisfying resolution to a non-tonic chord.